CBSE Class 12-science Answered
For cubic closed packed structure or FCC:
Contribution by atoms on the corners = 1/8 x 8 = 1 atom
Contribution by atoms on the faces = ½ x 6 = 3
Therefore, number of atoms present in the unit cell = 1+3 = 4 atoms
For hexagonal closest packed structure:
Contribution by atoms of the hex shape at top = 1/6 x 6 = 1 atom
Contribution by atoms of the hex shape at bottom = 1/6 x 6 = 1 atom
Contribution by the one atom at the centre of top and bottom hex each = 1
Contribution by the three atoms in the center = 3 atoms
Therefore, number of atoms per unit cell = 1+1+1+3 = 6 atoms
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